The quality of "to go" food available on airport concourses has improved so much over the last decade that it would still beat any domestic Y meal especially considering the increase in fare they would charge for the privilege of domestic Y dining systemwide on certain lengths. There is no free lunch.
To take it a step further, availability of domestic Delta One is also driven by competition.
DL's "hometown" airline has ZERO domestic D1 flights to/from ATL.
No Jet Blue Mint in ATL is one reason.
Competition on a given route affects the level of in-flight service in all cabins.